This invention relates to a low-temperature test equipment for testing or measuring electric characteristics of a specimen cooled in a vacuum atmosphere and the like, and more particularly to a low-temperature test equipment suitable for use as a semiconductor wafer test equipment for testing a semiconductor wafer.
In recent years, it has been highly demanded that a semiconductor device is subjected to measurement of electric characteristics thereof at an ultra-low temperature in a vacuum atmosphere for the purpose of ensuring reliable screening due to detection of abnormal leakage current which fails to be detected in a room temperature, checking of a low-temperature operation device such as a high-precision photo detector, measurement of physical characteristics of a device or pure wafer element at a low temperature to measure various characteristics thereof such as a concentration of impurities therein, and the like.
For this purpose, a test equipment is proposed in the art which includes a vacuum chamber formed so as to be evacuated at a vacuum by means of a vacuum pump, a wafer holder arranged in the vacuum chamber, an ultra-low temperature refrigerator having a cooling head positioned in the vacuum chamber, and the like. Also, another test equipment is known in the art, as disclosed in Japanese Patent Application Laid-Open Publication No. 137547/1992. The test equipment includes a vacuum chamber, a spare chamber arranged adjacently to the vacuum chamber and configured so as to communicate through a gate valve to the vacuum chamber and temporarily store a wafer which is an object to be tested (tested object) therein. The test equipment is so constructed that the spare chamber is evacuated at a vacuum when the wafer is accessed to the vacuum chamber and the gate valve is closed to increase a pressure in only the spare chamber to an atmospheric level when the wafer is removed from the spare chamber. This ensures that the vacuum chamber is constantly kept at a vacuum, to thereby subject the semiconductor wafer to a continuous test under ultra-low temperature conditions.
A test equipment for carrying out such a test at a normal temperature is generally constructed so as to monitor a procedure or situation of the test by means of a CCD camera, to thereby analyze an image of a surface of a semiconductor wafer and confirm a contact position of a distal end of a probe needle or a position at which the distal end is contacted with the semiconductor wafer. The CCD camera is required to provide an image at a high magnification and a narrow visual field in order to ensure that the contact position of the distal end of the probe needle is effectively confirmed, whereas it is required to provide an image at a low magnification and a wide visual field in order to ensure that an image of the surface of the semiconductor wafer is satisfactorily analyzed. Also, image-pickup or photographing by the CCD must be carried out through a hole of a probe card. Thus, the single CCD camera which includes a zoom lens has been conventionally used for this purpose.
However, in the above-described conventional test equipment at a low or ultra-low temperature, arrangement of the CCD camera including the zoom lens arranged in the vacuum chamber causes bursting of a lens receiving vessel, leading to production of gas from a motor for zooming, so that arrangement of the CCD camera in the vacuum chamber is rendered impossible.
Also, there are proposed techniques wherein two cameras are used in such a manner that one of the cameras is arranged above a hole of a probe card to analyze an image of a surface of a semiconductor wafer and the other camera is placed on a wafer holder to pick up an image of a probe needle from below. However, application of the techniques to the test equipment operated at a low or ultra-low temperature while setting the cameras on the wafer holder causes heat generated from the cameras to be transmitted to the wafer holder being cooled, to thereby adversely affect reliability of results of the test. Also, the wafer holder is cooled due to direct transmission of heat of the refrigerator thereto, so that arrangement of the camera on the wafer holder adversely affects operation of the camera, so that employment of the above-described techniques is substantially impossible.
Thus, the conventional test equipment operated at a low or ultra-low temperature fails to monitor a procedure or situation of the test by means of a image-pickup or photographing device such as a CCD camera or the like, resulting in positional registration or alignment between the probe needle and the semiconductor wafer being high difficult or substantially impossible. In particular, such a test equipment constructed so as to carry out continuous test operation fails to control operation of aligning the probe needle and semiconductor wafer with each other in association with monitoring operation as described above, leading to a failure in complete automation of the test.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a low-temperature test equipment which is capable of monitoring a test of a specimen by a prober under vacuum and low temperature or ultra-low temperature conditions.
It is another object of the present invention to provide a low-temperature test equipment which is capable of facilitating positional registration or alignment between probe needles and a specimen, to thereby ensure a test at high accuracy.
It is a further object of the present invention to provide a low-temperature test equipment which is capable of attaining full automation of a test when it is constructed so as to continuously carry out test operation.
It is still another object of the present invention to provide a low-temperature test equipment which is capable of being suitable for a test for a semiconductor wafer.
In accordance with the present invention, a low-temperature test equipment is provided. The low-temperature test equipment includes a vacuum chamber, a prober including a probe card and probe needles and arranged in the vacuum chamber, a specimen holder constructed to hold a specimen thereon and arranged in the vacuum chamber, a refrigerator having a cooling head arranged in the vacuum chamber, to thereby cool the specimen through the specimen holder prior to a test of the specimen by means of the prober, and a plurality of photographing means or image pickup means arranged above the specimen holder in the vacuum chamber in such a manner that plane positions thereof are different from each other. The photographing means are set at photographing magnifications different from each other, to thereby photograph a range of at least a part of at least one of the specimen which is an object to be photographed (photographed object) and the probe needles. The low-temperature test equipment further includes a prism mechanism arranged between the photographing means and the specimen holder to permit the photographing means different in plane position from each other to photograph the photographed object.
In a preferred embodiment of the present invention, the prism mechanism is arranged so as to permit image-pickup or photographing by each of the photographing means to be carried out through a hole of the probe card.
In a preferred embodiment of the present invention, the photographing means are set so as to permit one of the photographing means to photograph a distal end of the probe needles at a high magnification and a narrow visual field and the other photographing means to photograph a surface of the specimen at a low magnification and a wide visual field.
In a preferred embodiment of the present invention, the plural photographing means are arranged so as to be movable in three-dimensional directions.
In a preferred embodiment of the present invention, the photographing means each are constituted by a CCD camera.
In a preferred embodiment of the present invention, the low-temperature test equipment further includes a spare chamber connected through an openable gate valve to the vacuum chamber so that evacuation of the spare chamber at a vacuum and opening thereof to an atmosphere may be selectively carried out. The spare chamber is constructed so as to receive a plurality of the specimens therein and feed the specimens received therein to the specimen holder while constantly keeping the vacuum chamber at a vacuum, resulting in the specimen being tested successively.
In a preferred embodiment of the present invention, the specimen is a semiconductor wafer and the specimen holder is a wafer holder, whereby a semiconductor wafer supported on the wafer holder is subjected to a test.